Malignancy-associated hypercalcemia (MAHC) results from two general mechanisms: local osteolytic hypercalcemia and humoral hypercalcemia of malignancy. This proposal deals almost exclusively with the humoral syndrome, which appears to apply in some 80% of examples of human MAHC and for which several animal models have been discovered and/or developed. In ongoing studies, we have fully characterized the human humoral syndrome as well as that resulting from the H500 Leydig cell tumor in the Fisher rat and a novel murine squamous cell model in vivo. Material from human tumor extracts and Leydig cell conditioned medium have been purified more than 20,000-fold by conventional techniques. Messenger RNA has been prepared from human and animal model tumors and translated in in vitro and in vivo systems, with assay of translation products in several detection systems. The principal goals of the present proposal include: 1) to purify and analyze the factor(s) by conventional protein purification and analytical techniques, using material from a variety of sources, 2) to identify the factor(s) by receptor binding-displacement techniques, 3) to generate conventional and monoclonal antisera to the factor(s), 4) to fully characterize the apparent complete reversal of the syndrome in the Fisher rat produced by the infusion of a synthetic PTH analog, 5) to reproduce the syndrome in experimental animals and initiate physiological studies, and 6) to pursue molecular cloning of the factor(s) from both human and animal model tumors.